1. Field of the Invention
The present invention is related to automatic control of valve controlled equipment such as steam turbines and, more particularly, to a method for automatic calibration cf a steam turbine.
2. Description of the Related Art
There are many types of equipment and systems, from small engines up to entire plants, which include a system of valves controlled by an automatic controller. One example of such equipment is a steam turbine used to generate electricity. The amount of steam received by such a turbine from a boiler, heated by fossil fuel or a nuclear reactor, is controlled by inlet valves including throttle valves and governor valves. Typically, there are six to eight governor valves which are operated in one of two modes. In a single valve or unison mode, all the valves are opened at the same rate, while in a sequential mode, a group of valves are initially opened and then smaller groups of 1 to 3 valves are opened in sequence as additional flow is demanded.
Proper control of equipment, such as an electricity generating steam turbine, requires that the correspondence between valve settings and performance of the equipment or system be known. The designer of such equipment can determine the correspondence between the valve settings and the system performance with a degree of precision that varies depending on the complexity of the equipment or system and the environment or application in which the equipment is used. The use of feedback loops in automatic controllers is one way to correct for differences between the designed correspondence between valve settings and system operation and the actual operation under specific conditions. However, it is desirable to modify or make adjustments to the original correspondence between valve settings and system performance when the equipment is installed so that the delays involved in relying upon feedback loops can be reduced and the equipment can respond to changes in operating parameters more quickly and efficiently.
Conventionally, calibration of most valve controlled equipment, including steam turbines used for generating electricity, involves following a manual procedure to check the correspondence between specific valve settings and the system performance expected for those valve settings. Inevitably, there are variations in how the manual procedures are executed depending upon who performs the calibration and even variations by the same person over a period of time. In addition, the more complex the equipment or system, the more time consuming the calibration procedure becomes and a greater number of opportunities for variation are present.